Dual-cure method and system for fabrication of 3d polymeric structures cross-reference to earlier applications

ABSTRACT

A dual-cure method for forming a solid polymeric structure is provided. An end-capped, imide-terminated prepolymer is combined with at least one photopolymerizable olefinic monomer, at least one photoinitiator, and a diamine, to form a curable resin composition, which, in a first step, is irradiated under conditions effective to polymerize the at least one olefinic monomer, thus forming a scaffold composed of the prepolymer and the polyolefin with the diamine trapped therein. The irradiated composition is then thermally treated at a temperature effective to cause a transimidization reaction to occur between the prepolymer and the diamine, thereby releasing the end caps of the prepolymer and providing the solid polymeric structure. A curable resin composition comprising an end-capped, imide-terminated prepolymer, at least one photopolymerizable olefinic monomer, at least one photoinitiator, and a diamine, is also provided, as are related methods of use.

CROSS-REFERENCE TO EARLIER APPLICATIONS

This application claims priority under 35 USC 119(e) (1) to provisionalU.S. Patent Application Ser. This application is a divisional of U.S.patent application Ser. No. 16/732,178 filed Dec. 31, 2019 entitled“DUAL-CURE METHOD AND SYSTEM FOR FABRICATION OF 3D POLYMERICSTRUCTURES”, the disclosure of which are incorporated by referenceherein.

TECHNICAL FIELD

The invention relates generally to the fabrication of three-dimensionalobjects, and more particularly relates to the fabrication of 3Dstructures using a “dual cure” system.

BACKGROUND

Three-dimensional (3D) printing typically involves the production of 3Dobjects via an additive manufacturing (AM) process. Additivemanufacturing was originally developed in the early 1980s, and made useof UV-curable liquid resins to form thermoset polymers. A solidstructure was built up in layers, with each layer corresponding to across-sectional slice of the structure and formed by deposition andphotocure of the liquid resin. A stereolithographic additive (SLA)manufacturing process was developed several years later, in which across-sectional pattern of the object to be formed was created asdigital data, and the object then formed according to the pattern. Therehave been many developments in the field of 3D printing since then, andmany improvements and refinements have been made to the basic additivemanufacturing process:

Speed and accuracy have drastically improved, thus enabling themanufacture of extremely small or complex structures with extraordinaryprecision;

AM is currently implemented on a large-scale commercial level in manyfields of use, from the “bioprinting” of blood vessels and organs tointegrated circuit manufacture;

Fabrication of prototypes can be carried out quickly and inexpensivelyvia SLA “rapid prototyping,” a time- and cost-saving commercialadvantage; and the cost of 3D printing materials and equipment hasdropped to the point where the technology is accessible to individualsand small businesses as well as large organizations.

There remains a need for improvement, however, particularly with regardto the mechanical properties and surface finish of the manufacturedobject.

SUMMARY OF THE INVENTION

Accordingly, the invention is directed to methods and compositions thataddress the aforementioned need in the art.

In one embodiment, the invention provides a dual-cure method for forminga solid polymeric structure, the method comprising:

(a) combining an end-capped, imide-terminated prepolymer with at leastone photopolymerizable olefinic monomer, at least one photoinitiator,and a diamine, to form a curable resin composition;

(b) irradiating the resin composition under conditions effective topolymerize the at least one olefinic monomer and provide a polyolefinwithin a scaffold that comprises the prepolymer and the polyolefin withthe diamine physically trapped therein; and

(c) thermally treating the irradiated composition at a temperatureeffective to cause a transimidization reaction to occur between theprepolymer and the diamine, simultaneously releasing the end caps of theprepolymer, and providing the solid polymeric structure.

It will be appreciated that in the implementation of the aforementionedmethod in the 3D printing arena, the solid polymeric structurecorresponds to a 3D object of a predetermined shape and size as embodiedin a 3D printable model, such as may be generated using a computer-aideddesign (CAD) package, a 3D scanner, or photogrammetry software workingfrom a two-dimensional digital image.

In one aspect of the aforementioned embodiment, the curable resincomposition generated in step (a) is added to a build region thatdimensionally corresponds to the predetermined shape and size of theobject, prior to irradiation of the resin in step (b).

In another embodiment, a method is provided for forming a layer of a 3Dobject such as may be done in the context of an additive fabricationprocess. The method comprises:

(a) combining an end-capped, imide-terminated prepolymer with at leastone photopolymerizable olefinic monomer, at least one photoinitiator,and a diamine, to form a curable resin composition;

(b) providing the curable resin composition as a layer on a substrate,by coating, deposition, or other means; and

(c) irradiating the layer under conditions effective to polymerize theolefinic monomer and provide a polyolefin within a scaffold layer thatcomprises the prepolymer and the polyolefin with the diamine physicallytrapped therein.

In another embodiment, the invention provides an improved method forforming a 3D object using an additive fabrication process that comprisescomputer-controlled successive formation of layers on a substrate withdimensions corresponding to a 3D digital image, the improvement whichcomprises forming the layers by:

(a) providing an initial curable layer on a substrate, wherein the layercomprises a curable resin composition prepared by combining anend-capped, imide-terminated prepolymer, a photopolymerizable olefinicmonomer, at least one photoinitiator, and a diamine;

(b) irradiating the initial layer under conditions effective topolymerize the olefinic monomer and provide a polyolefin within a firstscaffold layer comprising the prepolymer and the polyolefin with thediamine physically trapped therein;

(c) repeating step (a) to provide an additional layer on the firstscaffold layer;

(d) irradiating the additional layer under conditions effective topolymerize the olefinic monomer and provide an additional scaffoldlayer;

(e) repeating steps (c) and (d) until formation of the 3D object iscomplete; and

(f) thermally treating the 3D object at a temperature effective to causea transimidization reaction to occur between the prepolymer and thediamine.

In one aspect of any of the aforementioned embodiments, the prepolymerhas the structure of Formula (I)

wherein:

L comprises an oligomeric hydrocarbylene moiety that is unsubstituted,substituted, heteroatom-containing, or substituted andheteroatom-containing;

Ar is aryl;

R¹ and R³ may be the same or different and are non-oligomeric linkinggroups;

q and r may be the same or different and are zero or 1; and

R² and R⁴ are imide end-capping groups that can be removed in atransimidization reaction.

In a related aspect, Ar is phenyl, such that the prepolymer has thestructure of Formula (II)

In another related aspect, the prepolymer has a weight average molecularweight in the range of about 500 to about 5000.

In another aspect of any of the above-delineated embodiments, thephotopolymerizable olefinic monomer serves as a reactive diluent.

In a related aspect, the photopolymerizable olefinic monomer is anacrylate or methacrylate monomer.

In another related aspect, the photopolymerizable olefinic monomer hasthe structure of Formula (XIV)

wherein:

R⁵ is H or CH₃ and R⁶ is C₁ to C₃₆ hydrocarbyl, substituted C₁ to C₃hydrocarbyl, heteroatom-containing C₁ to C₃ hydrocarbyl, or substitutedand heteroatom-containing C₁ to C₆ hydrocarbyl.

In an additional aspect of any of the above-delineated embodiments, thediamine serves as a chain extender and has the structure of Formula (XV)

H₂N-L¹-NH₂  (XV)

where L¹ is C₂ to C₁₄ hydrocarbylene, substituted C₂ to C₁₄hydrocarbylene, heteroatom-containing C₂ to C₁₄ hydrocarbylene, orsubstituted and heteroatom-containing C₂ to C₁₄ hydrocarbylene.

In another embodiment, the invention provides as a novel composition ofmatter a curable resin composition comprising an end-capped,imide-terminated prepolymer, at least one photopolymerizable olefinicmonomer, at least one photoinitiator, and a diamine.

In a further embodiment, the invention provides a method forsynthesizing the end-capped imide-terminated prepolymer, where thesynthetic method comprises:

(a) combining a diphthalic anhydride with an amine-terminated oligomerat a molar ratio of at least about 2:1 under conditions effective togive a phthalimide-terminated oligomer as a reaction product; and

(b) end-capping the phthalimide-terminated oligomer by admixing anamino-substituted cyclic reactant with the phthalimide-terminatedoligomer at a molar ratio of at least about 2:1 at an elevatedtemperature for a reaction time of at least about 12 hours.

In a further embodiment, the invention provides a dual-cure method forforming a solid polymeric structure, the method comprising:

(a) synthesizing an end-capped imide-terminated prepolymer by (i)combining a diphthalic anhydride with an amine-terminated oligomer at amolar ratio of at least about 2:1 under conditions effective to give aphthalimide-terminated oligomer as a reaction product, and (ii)end-capping the phthalimide-terminated oligomer by admixing anamino-substituted cyclic reactant with the phthalimide-terminatedoligomer at a molar ratio of at least about 2:1 at an elevatedtemperature for a reaction time of at least about 12 hours;

(b) combining the prepolymer with at least one photopolymerizableolefinic monomer, at least one photoinitiator, and a diamine, to form acurable resin composition;

(c) irradiating the resin composition under conditions effective topolymerize the at least one olefinic monomer and provide a polyolefinwithin a scaffold that comprises the prepolymer and the polyolefin withthe diamine physically trapped therein; and

(d) thermally treating the irradiated composition at a temperatureeffective to cause a transimidization reaction to occur between theprepolymer and the diamine, thereby releasing the end caps of theprepolymer and providing the solid polymeric structure.

In still another embodiment, a method is provided for forming a layer ofa three-dimensional object in an additive fabrication process,comprising:

(a) synthesizing an end-capped imide-terminated prepolymer by (i)combining a diphthalic anhydride with an amine-terminated oligomer at amolar ratio of at least about 2:1 under conditions effective to give aphthalimide-terminated oligomer as a reaction product, and (ii)end-capping the phthalimide-terminated oligomer by admixing anamino-substituted cyclic reactant with the phthalimide-terminatedoligomer at a molar ratio of at least about 2:1 at an elevatedtemperature for a reaction time of at least about 12 hours;

(b) combining the prepolymer with at least one photopolymerizableolefinic monomer, at least one photoinitiator, and a diamine, to form acurable resin composition;

(c) providing the curable resin composition as a layer on a substrate;and

(d) irradiating the layer under conditions effective to polymerize theolefinic monomer and provide a polyolefin within a scaffold layer thatcomprises the prepolymer and the polyolefin with the diamine physicallytrapped therein.

In another embodiment, the invention provides a photocured compositionprepared by irradiating a curable resin composition comprising anend-capped, imide-terminated prepolymer, at least one photopolymerizableolefinic monomer, at least one photoinitiator, and a diamine, withactinic radiation of a wavelength effective to cure thephotopolymerizable olefinic monomer.

In still a further embodiment, the invention provides a solidcomposition of matter prepared by: (a) irradiating a curable resincomposition comprising an end-capped, imide-terminated prepolymer, atleast one photopolymerizable olefinic monomer, at least onephotoinitiator, and a diamine, with actinic radiation of a wavelengtheffective to cure the photopolymerizable olefinic monomer, therebyproviding a photocured composition; and

(b) thermally treating the photocured composition provided in (a) withheat under conditions to facilitate a transimidization reaction betweenthe end-capped, imide-terminated prepolymer and the diamine.

DETAILED DESCRIPTION OF THE INVENTION 1. Nomenclature and Overview

Unless defined otherwise, all technical and scientific terms used hereinhave the meaning commonly understood by one of ordinary skill in the artto which the invention pertains. Specific terminology of particularimportance to the description of the present invention is defined below.

In this specification and the appended claims, the singular forms “a”,“an” and “the” include plural referents unless the context clearlydictates otherwise. Thus, for example, “a prepolymer” refers not only toa single prepolymer but also to a combination of two or more differentprepolymers, “a diamine” refers to a single diamine or to a combinationof diamines, and the like.

As used herein, the phrase “having the formula” or “having thestructure” is not intended to be limiting and is used in the same waythat the term “comprising” is commonly used.

The term “alkyl” as used herein refers to a branched or unbranchedsaturated hydrocarbon group containing 1 to about 24 carbon atoms, suchas methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl,octyl, decyl, and the like, as well as cycloalkyl groups such ascyclopentyl, cyclohexyl, and the like. Generally, although again notnecessarily, alkyl groups herein contain 1 to about 18 carbon atoms,preferably 1 to about 12 carbon atoms. The term “lower alkyl” intends analkyl group of 1 to 6 carbon atoms. Preferred lower alkyl substituentscontain 1 to 3 carbon atoms, and particularly preferred suchsubstituents contain 1 or 2 carbon atoms (i.e., methyl and ethyl).“Substituted alkyl” refers to alkyl substituted with one or moresubstituent groups, and the terms “heteroatom-containing alkyl” and“heteroalkyl” refer to alkyl in which at least one carbon atom isreplaced with a heteroatom, e.g., O, S, or N. If not otherwiseindicated, the terms “alkyl” and “lower alkyl” include linear, branched,cyclic, unsubstituted, substituted, and/or heteroatom-containing alkylor lower alkyl, respectively.

The term “alkylene” as used herein refers to a difunctional linear,branched, or cyclic saturated hydrocarbon linkage containing 1 to about24 carbon atoms, such as methylene, ethylene, n-propylene, n-butylene,n-hexylene, decylene, tetradecylene, hexadecylene, and the like.Preferred alkylene linkages contain 1 to about 12 carbon atoms, and theterm “lower alkylene” refers to an alkylene linkage of 1 to 6 carbonatoms, preferably 1 to 4 carbon atoms. The term “substituted alkylene”refers to an alkylene linkage substituted with one or more substituentgroups, i.e., wherein a hydrogen atom is replaced with a non-hydrogensubstituent group, and the terms “heteroatom-containing alkylene” and“heteroalkylene” refer to alkylene linkages in which at least one carbonatom is replaced with a heteroatom. If not otherwise indicated, theterms “alkylene” and “lower alkylene” include linear, branched, cyclic,unsubstituted, substituted, and/or heteroatom-containing alkylene andlower alkylene, respectively. Oligomeric and polymeric “alkylenes” arealso envisioned herein, such as, for example, a substituted orunsubstituted, optionally heteroatom-containing poly(ethylene).

The term “alkenyl” as used herein refers to a linear, branched or cyclichydrocarbon group of 2 to about 24 carbon atoms containing at least onedouble bond, such as ethenyl, n-propenyl, isopropenyl, n-butenyl,isobutenyl, octenyl, decenyl, tetradecenyl, hexadecenyl, eicosenyl,tetracosenyl, and the like. Generally, although again not necessarily,alkenyl groups herein contain 2 to about 18 carbon atoms, preferably 2to 12 carbon atoms. The term “lower alkenyl” intends an alkenyl group of2 to 6 carbon atoms, and the specific term “cycloalkenyl” intends acyclic alkenyl group, preferably having S to 8 carbon atoms. The term“substituted alkenyl” refers to alkenyl substituted with one or moresubstituent groups, and the terms “heteroatom-containing alkenyl” and“heteroalkenyl” refer to alkenyl in which at least one carbon atom isreplaced with a heteroatom. If not otherwise indicated, the terms“alkenyl” and “lower alkenyl” include linear, branched, cyclic,unsubstituted, substituted, and/or heteroatom-containing alkenyl andlower alkenyl, respectively.

The term “alkenylene” as used herein refers to a difunctional linear,branched, or cyclic hydrocarbon linkage containing 2 to about 24 carbonatoms, such as ethenylene, n-propenylene, isopropenylene, n-butenylene,isobutenylene, octenylene, decenylene, tetradecenylene, hexadecenylene,eicosenylene, tetracosenylene, etc. Preferred alkenylene linkagescontain 2 to about 12 carbon atoms, and the term “lower alkylene” refersto an alkylene linkage of 2 to 6 carbon atoms, preferably 2 to 4 carbonatoms. The term “substituted alkenylene” refers to an alkenylene linkagesubstituted with one or more substituent groups, i.e., wherein ahydrogen atom is replaced with a non-hydrogen substituent group, and theterms “heteroatom-containing alkenylene” and “heteroalkenylene” refer toalkenylene linkages in which at least one carbon atom is replaced with aheteroatom. If not otherwise indicated, the terms “alkylene” and “loweralkenylene” include linear, branched, cyclic, unsubstituted,substituted, and/or heteroatom-containing alkenylene and loweralkenylene, respectively. Oligomeric and polymeric “alkenylene linkages”are also envisioned herein, such as, for example, a substituted orunsubstituted, optionally heteroatom-containing poly(ethylene) linker,which may form the body of an oligomer or polymer that bridges two endgroups.

The term “aryl” as used herein, and unless otherwise specified, refersto an aromatic substituent containing a single aromatic ring or multiplearomatic rings that are fused together, directly linked, or indirectlylinked (such that the different aromatic rings are bound to a commongroup such as a methylene or ethylene moiety). Preferred aryl groupscontain 5 to 24 carbon atoms, and particularly preferred aryl groupscontain 5 to 14 carbon atoms. Exemplary aryl groups contain one aromaticring or two fused or linked aromatic rings, e.g., phenyl, naphthyl,biphenyl, diphenylether, diphenylamine, benzophenone, and the like.“Substituted aryl” refers to an aryl moiety substituted with one or moresubstituent groups, and the terms “heteroatom-containing aryl” and“heteroaryl” refer to aryl substituent, in which at least one carbonatom is replaced with a heteroatom, as will be described in furtherdetail infra. If not otherwise indicated, the term “aryl” includesunsubstituted, substituted, and/or heteroatom-containing aromaticsubstituents.

The term “arylene” refers to a bivalent aromatic group, containing oneto three aromatic rings, either fused or linked, and eitherunsubstituted or substituted with one or more substituents. Unlessotherwise indicated, the term “arylene” includes substituted aryleneand/or heteroatom-containing arylene.

The term “alkaryl” refers to an aryl group with an alkyl substituent,and the term “aralkyl” refers to an alkyl group with an arylsubstituent, wherein “aryl” and “alkyl” are as defined above. Preferredaralkyl groups contain 6 to 24 carbon atoms, and particularly preferredaralkyl groups contain 6 to 16 carbon atoms. Examples of aralkyl groupsinclude, without limitation, benzyl, 2-phenyl-ethyl, 3-phenyl-propyl,4-phenyl-butyl, 5-phenyl-pentyl, 4-phenylcyclohexyl, 4-benzylcyclohexyl,4-phenylcyclohexylmethyl, 4-benzylcyclohexylmethyl, and the like.Alkaryl groups include, for example, p-methylphenyl, 2,4-dimethylphenyl,p-cyclohexylphenyl, 2,7-dimethylnaphthyl, 7-cyclooctyinaphthyl,3-ethyl-cyclopenta-1,4-diene, and the like. The terms “alkaryloxy” and“aralkyloxy” refer to substituents of the formula —OR wherein R isalkaryl or aralkyl, respectively, as just defined.

The term “acyl” refers to substituents having the formula —(CO)-alkyl,—(CO)-aryl, or —(CO)-aralkyl, and the term “acyloxy” refers tosubstituents having the formula —O(CO)— alkyl, —O(CO)-aryl, or—O(CO)-aralkyl, wherein “alkyl”, “aryl” and “aralkyl” are as definedabove.

The term “cyclic” refers to alicyclic or aromatic substituents that mayor may not be substituted and/or heteroatom containing, and that may bemonocyclic, bicyclic, or polycyclic.

The term “alicyclic” is used in the conventional sense to refer to analiphatic cyclic moiety, as opposed to an aromatic cyclic moiety, andmay be monocyclic, bicyclic, or polycyclic. Alicyclic compounds orsubstituents may be heteroatom-containing and/or substituted, but arenormally unsubstituted and do not contain heteroatoms, i.e., arecarbocyclic.

The term “heteroatom-containing” as in a “heteroatom-containing alkylgroup” (also termed a “heteroalkyl” group) or a “heteroatom-containingaryl group” (also termed a “heteroaryl” group) refers to a molecule,linkage or substituent in which one or more carbon atoms are replacedwith an atom other than carbon, e.g., nitrogen, oxygen, sulfur,phosphorus or silicon, typically nitrogen, oxygen or sulfur, preferablynitrogen or oxygen. Similarly, the term “heteroalkyl” refers to an alkylsubstituent that is heteroatom-containing, the term “heterocyclic”refers to a cyclic substituent that is heteroatom-containing, the terms“heteroaryl” and heteroaromatic” respectively refer to “aryl” and“aromatic” substituents that are heteroatom-containing, and the like.Examples of heteroalkyl groups include alkoxyaryl,alkylsulfanyl-substituted alkyl, N-alkylated amino alkyl, and the like.Examples of heteroaryl substituents include pyrrolyl, pyrrolidinyl,pyridinyl, quinolinyl, indolyl, pyrimidinyl, imidazolyl,1,2,4-triazolyl, tetrazolyl, etc., and examples of heteroatom-containingalicyclic groups are pyrrolidino, morpholino, piperazino, piperidino,etc.

“Hydrocarbyl” refers to univalent hydrocarbyl radicals containing 1 toabout 30 carbon atoms, preferably 1 to about 24 carbon atoms, morepreferably 1 to about 18 carbon atoms, most preferably about 1 to 12carbon atoms, including linear, branched, cyclic, saturated, andunsaturated species, such as alkyl groups, alkenyl groups, aryl groups,and the like. “Substituted hydrocarbyl” refers to hydrocarbylsubstituted with one or more substituent groups, and the term“heteroatom-containing hydrocarbyl” refers to hydrocarbyl in which atleast one carbon atom is replaced with a heteroatom. Unless otherwiseindicated, the term “hydrocarbyl” is to be interpreted as includingsubstituted and/or heteroatom-containing hydrocarbyl moieties.

The term “hydrocarbylene” intends a divalent hydrocarbyl moietycontaining 1 to about 24 carbon atoms, most preferably 1 to about 12carbon atoms, including linear, branched, cyclic, saturated andunsaturated species, and the term “lower hydrocarbylene” intends ahydrocarbylene group of 1 to 6 carbon atoms, preferably 1 to 4 carbonatoms. The term “substituted hydrocarbyl” refers to hydrocarbylsubstituted with one or more substituent groups, and the terms“heteroatom-containing hydrocarbyl” and “heterohydrocarbyl” refer tohydrocarbyl in which at least one carbon atom is replaced with aheteroatom. Similarly, “substituted hydrocarbylene” refers tohydrocarbylene substituted with one or more substituent groups, and theterms “heteroatom-containing hydrocarbylene” and “heterohydrocarbylene”refer to hydrocarbylene in which at least one carbon atom is replacedwith a heteroatom. Unless otherwise indicated, the terms “hydrocarbyl”and “hydrocarbylene” are to be interpreted as including substitutedand/or heteroatom-containing hydrocarbyl and hydrocarbylene moieties,respectively. Oligomeric and polymeric hydrocarbylene moieties are alsoenvisioned, including heteroatom-containing hydrocarbylenes such aspoly(ethylene oxide) and substituted analogs thereof.

When a functional group is termed “protected” or “capped,” as in an“end-capped” group, this means that the group is in modified form topreclude undesired reactions and/or promote a desired reaction. Suitableprotecting groups for the compounds of the present invention will berecognized from the present application taking into account the level ofskill in the art, and with reference to standard textbooks, such asGreene et al., Protective Groups in Organic Synthesis (New York: Wiley,1991).

By “substituted” as in “substituted alkyl”, “substituted aryl” and thelike, as alluded to in some of the aforementioned definitions, is meantthat in the alkyl, aryl, or other moiety, at least one hydrogen atombound to a carbon (or other) atom is replaced with one or morenon-hydrogen substituents. Examples of such substituents include,without limitation: functional groups such as halo, hydroxyl,sulfhydryl, C₁-C₂₄ alkoxy, C₂-C₂ alkenyloxy, C₂-C₂₄ alkynyloxy, C₅-C₂₄aryloxy, acyl (including C₂-C₂₄ alkylcarbonyl (—CO-alkyl) and C₆-C₂₄arylcarbonyl (—CO-aryl)), acyloxy (—O-acyl), C₂-C₂₄ alkoxycarbonyl(—(CO)—O-alkyl), C₆-C₂₄ aryloxycarbonyl (—(CO)—O-aryl), halocarbonyl(—CO)—X where X is halo), C₂-C₂₄ alkylcarbonato (—O—(CO)—O-alkyl),C₆-C₂₄ arylcarbonato (—O—(CO)—O-aryl), carboxy (—COOH), carboxylato(—COO—), carbamoyl (—(CO)—NH₂), mono-(C₁-C₂₄ alkyl)-substitutedcarbamoyl (—(CO)—NH(C₁-C₂₄ alkyl)), di-(C₁-C₂₄ alkyl)-substitutedcarbamoyl (—(CO)—N(C₁-C₂₄ alkyl)₂), mono-(C₆-C₂₄ aryl)-substitutedcarbamoyl (—(CO)—NH-aryl), di-(C₆-C₂₄ aryl)-substituted carbamoyl(—(CO)—N(aryl)₂), di-N—(C₁-C₂₄ alkyl), N—(C₆-C₂₄ aryl)-substitutedcarbamoyl, thiocarbamoyl (—(CS)—NH₂), carbamide (—NH—(CO)—NH₂),cyano(-C≡N), isocyano (—N⁺≡C⁻), cyanato (—O—C≡N), isocyanato (—O—N⁺≡C⁻),isothiocyanato (—S—C≡N), azido (—N═N⁺≡N⁻), formyl (—(CO)—H), thioformyl(—(CS)—H), amino (—NH₂), mono-(C₁-C₂₄ alkyl)-substituted amino,di-(C₁-C₂₄ alkyl)-substituted amino, mono-(C₅-C₂₄ aryl)-substitutedamino, di-(C₅-C₂₄ aryl)-substituted amino, C₂-C₂₄ alkylamido(—NH—(CO)-alkyl), C₆-C₂ arylamido (—NH—(CO)-aryl), imino (—CR═NH whereR=hydrogen, C₁-C₂₄ alkyl, C₅-C₂₄ aryl, C₆-C₂₄ alkaryl, C₆-C₂₄ aralkyl,etc.), alkylimino (—CR═N(alkyl), where R-hydrogen, C₁-C₂₄ alkyl, C₅-C₂₄aryl, C₆-C₂₄ alkaryl, C₆-C₂₄ aralkyl, etc.), arylimino (—CR═N(aryl),where R=hydrogen, C₁-C₂₄ alkyl, C₅-C₂₄ aryl, C₆-C₂₄ alkaryl, C₆-C₂₄aralkyl, etc.), nitro (—NO₂), nitroso (—NO), sulfo (—SO₂—OH), sulfonato(—SO₂—O—), C₁-C₂₄ alkylsulfanyl (—S-alkyl; also termed “alkylthio”),arylsulfanyl (—S-aryl; also termed “arylthio”), C₁-C₂₄ alkylsulfinyl(—(SO)-alkyl), C₅-C₂₄ arylsulfinyl (—(SO)-aryl), C₁-C₂₄ alkylsulfonyl(—SO₂-alkyl), C₅-C₂₄ arylsulfonyl (—SO₂-aryl), phosphono (—P(O)(OH)₂),phosphonato (—P(O)(O—)₂), phosphinato (—P(O)(O—)), phospho (—PO₂), andphosphino (—PH₂); and the hydrocarbyl moieties C₁-C₂₄ alkyl (preferablyC₁-C₁₈ alkyl, more preferably C₁-C₁₂ alkyl, most preferably C₁-C₆alkyl), C₂-C₂₄ alkenyl (preferably C₂-C₁₈ alkenyl, more preferablyC₂-C₁₂ alkenyl, most preferably C₂-C₆ alkenyl), C₂-C₂ alkynyl(preferably C₂-C₁₈ alkynyl, more preferably C₂-C₁₂ alkynyl, mostpreferably C₂-C₆ alkynyl), C₅-C₂₄ aryl (preferably C₅-C₁₄ aryl), C₆-C₂₄alkaryl (preferably C₆-C₁₈ alkaryl), and C₆-C₂₄ aralkyl (preferablyC₆-C₁₈ aralkyl).

In addition, the aforementioned functional groups may, if a particulargroup permits, be further substituted with one or more additionalfunctional groups or with one or more hydrocarbyl moieties such as thosespecifically enumerated above. Analogously, the above-mentionedhydrocarbyl moieties may be further substituted with one or morefunctional groups or additional hydrocarbyl moieties such as thosespecifically enumerated.

The term “polymer” is used to refer to a chemical compound thatcomprises linked monomers, and that may be straight, branched, orcrosslinked. The term also encompasses homopolymers, copolymers,terpolymers, tetrapolymers, and the like. Any polymers identified ascontaining more than one type of recurring unit, i.e., a copolymer,terpolymer, tetrapolymer, or the like, are not intended to be limitedwith respect to configuration. That is, for example, copolymers hereinmay be block copolymers, alternating copolymers, random copolymers,terpolymers may be block terpolymers, random terpolymers, and the like.The term “oligomer” refers to a lower molecular weight, linear polymerthat can participate in one or more reactions with itself or with othercompounds, e.g., monomers and/or other oligomers, to form a highermolecular weight polymer structure.

When the term “substituted” appears prior to a list of possiblesubstituted groups, it is intended that the term apply to every memberof that group. For example, the phrase “substituted alkyl, alkenyl, andaryl” is to be interpreted as “substituted alkyl, substituted alkenyl,and substituted aryl”. Analogously, when the term“heteroatom-containing” appears prior to a list of possibleheteroatom-containing groups, it is intended that the term apply toevery member of that group. For example, the phrase“heteroatom-containing alkyl, alkenyl, and aryl” is to be interpreted as“heteroatom-containing alkyl, substituted alkenyl, and substitutedaryl”.

“Optional” or “optionally” means that the subsequently describedcircumstance may or may not occur, so that the description includesinstances where the circumstance occurs and instances where it does not.For example, the phrase “optionally substituted” means that anon-hydrogen substituent may or may not be present on a given atom, and,thus, the description includes structures wherein a non-hydrogensubstituent is present and structures wherein a non-hydrogen substituentis not present. Similarly, the phrase an “optionally present” bond asindicated by a dotted line - - - - - in the chemical formulae hereinmeans that a bond may or may not be present.

In one embodiment, then, the invention provides a curable resincomposition by combining (i) an end-capped, imide-terminated prepolymerwith (ii) a photopolymerizable olefinic monomer, (iii) at least onephotoinitiator, and (iv) a diamine; in another embodiment, the inventionprovides a method for synthesizing the end-capped, imide-terminatedprepolymer. The curable resin composition is useful in a dual-curemethod for forming a solid polymeric structure, such as in the contextof an additive manufacturing process or other method of “3D” printing.The first step of the dual-cure method comprises irradiating the curableresin composition under conditions effective to polymerize the olefinicmonomer and provide a polyolefin within a scaffold that comprises theprepolymer and the polyolefin, with the diamine physically trappedtherein. In a second step, the photocured composition, i.e., thescaffold formed upon photopolymerization, is thermally treated underconditions effective to facilitate a transimidization reaction betweenthe prepolymer and the diamine, thereby releasing the end caps of theprepolymer and providing a final polymeric structure that has superiormechanical properties and optimal surface characteristics

2. The Photocurable Resin Composition

A. The Prepolymer.

The end-capped, imide-terminated prepolymer has the structure of Formula(I)

wherein:

L comprises an oligomeric hydrocarbylene moiety, and may beunsubstituted, substituted with one or more non-carbon, non-hydrogensubstituents and/or functional groups as explained in Section 1 of thisDetailed Description, heteroatom-containing, or both substituted andheteroatom-containing. Accordingly. L can be alkylene, substitutedalkylene, heteroalkylene, substituted alkylene, where any heteroatomspresent ae typically selected from nitrogen, oxygen, and sulfur, butmost typically are oxygen atoms. An example of an alkylene “L” is anoligomeric form of polyethylene, and an example of a heteroalkylene “L”is an oligomeric form of poly(ethylene oxide), such that L is

respectively.

where “n” represents the number of the monomer units contained within L.The number of monomer units is generally chosen to provide theprepolymer with a weight average molecular weight in the range of about500 to about 5000, typically in the range of about 1000 to about 3000.

Ar is aryl, and includes, as explained in the preceding section,unsubstituted aryl, substituted aryl, heteroaryl, and substitutedheteroaryl, where Ar may be monocyclic, bicyclic, or polycyclic,wherein, if bicyclic or polycyclic, the rings can be fused or linked.The two Ar moieties shown in Formula ( ) may be the same or different,but ae typically the same. When Ar is phenyl, the prepolymer has thestructure of Formula (II)

In Formula (II), it can be seen that the two end groups are phthalimidemoieties that are N-substituted with R² or R⁴, wherein R² and R⁴ areimide end-capping groups that are removed in the transimidizationreaction. That is, R² and R⁴ are selected so that the followingtransimidization reaction can proceed upon heating (the reaction isshown in simplified form for illustrative purposes, with only oneterminus of the prepolymer shown and a monofunctional R—NH₂ reactantinstead of the diamine)

The imide end-capping groups R² and R⁴ are generally the same, tofacilitate prepolymer synthesis as will be described infra. However, itwill be appreciated that the invention does not require that R² and R⁴be identical.

R¹ and R³ are optional non-oligomeric linking groups, insofar as r and qare independently selected from zero and 1. As with the end-cappinggroups R² and R⁴, it is preferred although not essential that r and qare the same and, when r and q are 1, that R¹ and R³ are the same aswell.

In some embodiments, R¹ and R³ comprise phthalimide groups, such thatthe prepolymer has the structure of Formula (II)

wherein s and t are independently selected from zero and 1, although ina preferred embodiment s and t are the same. X and Y are independentlyselected from O, S, end lower alkylene (e.g., substituted orunsubstituted methylene, ethylene, n-propylene or n-butylene), although,again, X and Y are preferably the same. When s and t are zero, theprepolymer of Formula (III) has the structure of Formula (IV)

When L is poly(ethylene oxide), the prepolymer of Formula (IV) has thestructure shown in Formula (V)

while when L is poly(ethylene), it will be appreciated that theprepolymer of Formula (IV) has the structure of Formula (VI)

When s and t we 1 and X and Y we both O, the prepolymer of Formula (III)has the structure of Formula (VII)

wherein when L is poly(ethylene oxide) or poly(ethylene), the prepolymerof Formula (VII) has the structure of Formula (VIII) or Formula (IX),respectively.

The imide end-capping groups R² and R⁴, as explained above, are selectedto enable a transimidization reaction to occur with the diamine any suchend-capping groups may be advantageously used herein, provided that theyfacilitate transimidization and do not adversely interact with anycomponents of the curable resin composition or have an adverse impact onthe final product.

In some embodiments, the R² and R⁴ end-capping moieties are the same andare five- to six-membered cyclic groups containing 1 to 4, preferably 1to 3, most preferably 1 or 2 heteroatoms, wherein at least one of theheteroatoms is a nitrogen atom and further wherein the ring nitrogen ofthe phthalimide group is directly bound to a carbon atom of theend-capping moiety. Examples of such end-capping moieties include,without limitation, nitrogen-containing heterocyclic substituents suchas pyridinyl, bipyridinyl, pyridazinyl, pyrimidinyl, bipyridaminyl,pyrazinyl, 1,3,5-triazinyl, 1,2,4-triazinyl, 1,2,3-triazinyl, pyrrolyl,2H-pyrrolyl, 3H-pyrrolyl, pyrazolyl, 2H-imidazolyl, 1,2,3-triazolyl,1,2,4-triazolyl, indolyl, 3H-indolyl, 1H-isoindolyl,cyclopenta(b)pyridinyl, indazolyl, quinolinyl, bisquinolinyl,isoquinolinyl, bisisoquinolinyl, cinnolinyl, quinazolinyl,naphthyndinyl, piperidinyl, piperazinyl, pyrrolidinyl, pyrazolidinyl,quinuclidinyl, imidazolidinyl, picolyliminyl, purinyl, benzimidazolyl,bisimidazolyl, phenazinyl, acridinyl, and carbazolyl. Preferred nitrogenheterocycles suitable as the imide end-capping groups are aryl, thusincluding pyrrolyl, imidazolyl, pyrazolyl, triazolyl, pyridinyl,pyrimidinyl, pyridazinyl, and pyrazinyl, as well as substituted analogsthereof.

Representative prepolymers of the invention in which R² and R arepyrimidinyl are shown in the following Formulae (X) through (XI):

Ideally, the prepolymer has a weight average molecular weight in therange of about 500 to about 5000, typically in the range of about 1000to about 3000.

B. The Photopolymerizable Olefinic Monomer:

The photopolymerizable olefinic monomer serves as a reactive diluentand, upon irradiation, polymerizes and thereby facilitates formation ofa stable, homogeneous network, or scaffold, which can then be thermallytreated to form a final polymeric product. In some embodiments, thephotopolymerizable olefinic monomer that serves as reactive diluent isan acrylate or methacrylate monomer. In other embodiments, the olefinicmonomer comprises a vinyl ester such as vinyl acetate; vinyl chloride;vinyl alcohol; vinyl toluene; styrene; acrylonitrile; propene;butadiene; cyclohexene; or divinyl benzene. It is to be understood thatthe foregoing monomers are merely illustrative and not limiting;virtually any photopolymerizable olefinic monomer can be advantageouslyused in conjunction with the present invention.

In some embodiments, the photopolymerizable olefinic monomer, as notedabove, is an acrylate or methacrylate monomer, which may bemonofunctional, difunctional, or polyfunctional.

By “monofunctional” is meant that the acrylate or methacrylate monomerhas one alkenyl functionality, with that functionality being the doublebond contained within the acrylate moiety (i.e., the ═CH₂ at the carbonatom alpha to the carbonyl carbon), although the monomer may compriseone or more aryl moieties. The term “acrylate monomer” as used hereinencompasses acrylates and methacrylates, i.e., esters of acrylic acidand methacrylic acid, respectively, as well as higher order acrylic acidesters such as ethyl acrylate, butyl acrylate, and the like.Methacrylates may in some embodiments be preferred relative toacrylates, however, insofar as the photopolymerization reaction (1)tends to proceed in a more controlled fashion with methacrylate monomersrelative to acrylate monomers, and (2) may ultimately produce a productthat has more desirable mechanical properties and surface finish.

In one embodiment, a photopolymerizable, monofunctional acrylate monomerhas the structure of Formula (XIV)

wherein R⁵ is H or methyl, such that the monomer is an acrylate or amethacrylate, respectively, and R⁶ is C₁ to C₃₆ hydrocarbyl, substitutedC₁ to C₃₆ hydrocarbyl, heteroatom-containing C₁ to C₃₆ hydrocarbyl, orsubstituted and heteroatom-containing C₁ to C₃₆ hydrocarbyl, and istypically C₁ to C₂₄ hydrocarbyl, substituted C₁ to C₂₄ hydrocarbyl,heteroatom-containing C₁ to C₂₄ hydrocarbyl, or substituted andheteroatom-containing C₁ to C₂₄ hydrocarbyl, such as C₂ to C₁₆hydrocarbyl, substituted C₂ to C₁₆ hydrocarbyl, heteroatom-containing C₂to C₁₆ hydrocarbyl, or substituted and heteroatom-containing C₂ to C₁₆hydrocarbyl, or C₄ to C₁₂ hydrocarbyl, substituted C₄ to C₁₂hydrocarbyl, heteroatom-containing C₄ to C₁₂ hydrocarbyl, or substitutedand heteroatom-containing C₄ to C₁₂ hydrocarbyl. Within theaforementioned categories. R⁵ may be, by way of example, C₁ to C₃₆alkyl, substituted C₁ to C₃₆ alkyl, heteroatom-containing C₁ to C₃₆alkyl, or substituted and heteroatom-containing C₁ to C₃₆ alkyl, andtypically C₁ to C₂₄ alkyl, substituted C₁ to C₂₄ alkyl,heteroatom-containing C₁ to C₂₄ alkyl, or substituted andheteroatom-containing C₁ to C₂₄ alkyl, such a C₂ to C₁₆ alkyl,substituted C₂ to C₁₆ alkyl, heteroatom-containing C₂ to C₁₆ alkyl, orsubstituted and heteroatom-containing C₂ to C₁₆ alkyl, or C₄ to C₁₂alkyl, substituted C₄ to C₁₂ alkyl, heteroatom-containing C₄ to C₁₂alkyl, or substituted and heteroatom-containing C₄ to C₁₂ alkyl. Asnoted above, the R⁵ moiety can also be aryl, including unsubstitutedaryl, substituted aryl, heteroaryl, substituted heteroaryl,unsubstituted aralkyl, substituted aralkyl, heteroaralkyl, substitutedheteroaralkyl, such as C₅ to C₃₆ unsubstituted aryl, substituted C₅ toC₃₆ aryl, C₂ to C₃₆ heteroaryl, substituted C₂ to C₃₆ heteroaryl,unsubstituted C₆ to C₃₆ aralkyl, substituted C₆ to C₃₆ aralkyl, C₃ toC₃₆ heteroaralkyl, substituted C₃ to C₃₆ heteroaralkyl, typically C₅ toC₂₄ unsubstituted aryl, substituted C₅ to C₂₄ aryl, C₂ to C₂₄heteroaryl, substituted C₂ to C₂₄ heteroaryl, unsubstituted C₆ to C₂₄aralkyl, substituted C₆ to C₂₄ aralkyl, C₃ to C₂₄ heteroaralkyl,substituted C₃ to C₂ heteroaralkyl, such as C₅ to C₁₆ unsubstitutedaryl, substituted C₅ to C₁₆ aryl, C₂ to C₁₆ heteroaryl, substituted C₂to C₁₆ heteroaryl, unsubstituted C₆ to C₁₆ aralkyl, substituted C₆ toC₁₆ aralkyl, C₃ to C₁₆ heteroaralkyl, substituted C₃ to C₁₆heteroaralkyl, or C₅ to C₁₂ unsubstituted aryl, substituted C₅ to C₁₂aryl, C₂ to C₁₂ heteroaryl, substituted C₂ to C₁₂ heteroaryl,unsubstituted C₆ to C₁₂ aralkyl, substituted C₆ to C₁₂ aralkyl, C₃ toC₁₂ heteroaralkyl, substituted C₃ to C₁₂ heteroaralkyl. Any heteroatomsare usually N or O, and aryl groups are usually, but not necessarily,monocyclic; fused and linked bicyclic or tricyclic groups are alsocontemplated.

In some embodiments, R⁶ comprises a C₆-C₃₆ alicyclic moiety, typically abridged (bicyclic or polycyclic) C₆-C₃₆ alicyclic moiety, and may besubstituted and/or heteroatom-containing R⁶ thus includes optionallysubstituted and/or heteroatom-containing C₆-C₂₄ alicyclic and C₆-C₁₆alicyclic groups. Non-limiting examples of such groups suitable as R⁵include adamantyl, 2-methyl-2-adamantyl, 2-ethyl-2-adamantyl,5-hydroxy-2-methyl-2-adamantyl, 5-hydroxy-2-ethyl-2-adamantyl,1-methyl-1-adamantylmethyl, 2-methyl-2-norbornyl, 2-ethyl-2-norbornyl,1,2,7,7-tetramethyl-2-norbornyl, isobornyl, and the like.

Specific examples of photocurable monofunctional acrylate andmethacrylate monomers thus include, without limitation, isobornylacrylate, isobornyl methacrylate, adamantyl acrylate, adamantylmethacrylate, isodecyl acrylate, isodecyl methacrylate, lauryl acrylate,lauryl methacrylate, 3,3,5-trimethylcyclohexane acrylate,3,3,5-trimethylcyclohexane methacrylate, (2-(2-ethoxyethoxy) ethylacrylate, (2-(2-ethoxyethoxy) ethyl methacrylate, cyclictrimethylolpropane formal acrylate, cyclic trimethylolpropane formalmethacrylate, tetrahydrofurfuryl acrylate, tetrahydrofurfurylmethacrylate, tridecyl acrylate, tridecyl methacrylate, 2-phenoxy ethylacrylate, and 2-phenoxy ethyl methacrylate. Other examples will beapparent to those of ordinary skill in the art or can be found in thepertinent texts and literature. See, e.g., U.S. Pat. No. 7,041,846 toWatanabe et al., the disclosure of which is incorporated herein withregard to monofunctional acrylate and methacrylate monomers.

Difunctional acrylate and methacrylate moieties useful in conjunctionwith the present methods and compositions include tripropyleneglycoldiacrylate, 1,6-hexanediol diacrylate, tricyclodecane dimethanoldiacrylate, diethyleneglycol dimethacrylate, dipropyleneglycoldiacrylate, difunctional glycol acrylate, ethoxylated bisphenol Adiacrylates, propoxylated neopentylglycol diacrylates, neopentylglycoldiacrylate, and ethyleneglycol dimethacrylate, while examples ofpolyfunctional acrylates and methacrylates suitable for use hereininclude trimethylpropane triacrylate, trimethylpropane trimethacrylate,ethoxylated trimethylpropane triacrylates, propoxylated glyceryltriacrylates, tris-(2-hydroxyethyl) isocyanurate triacrylate,pentaerythritol triacrylate, ethoxylated pentaerythritol tetraacrylates,trimethylolpropane triacrylate (TMPTA), di(trimethylolpropane)tetraacrylate, dipentaerythritol hexaacrylate, and dipentaerythritolhexaacrylate.

C. Polymerization Initiators:

Another component of the curable resin composition is aphotopolymerization initiator, or “photoinitiator”. As the initial stepin the dual-cure process requires photopolymerization of the olefinicmonomer, the curable resin composition comprises at least onephotoinitiator, i.e., a free radical photoinitiator. The free radicalphotoinitiator may be, by way of illustration and not limitation: anacylphosphine oxide, such as 2,4,6-trimethylbenzoylethoxyphenylphosphineoxide) (TEPO), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO),bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide, or the like; anα-hydroxy ketone, such as 2-hydroxy-2-methyl-1-phenyl acetone,1-hydroxy-cyclohexyl benzophenone,2-hydroxy-2-methyl-1-p-hydroxyethylether phenyl acetone, etc.; adiarylketone such as benzophenone, 2,2-dimethoxy-2-phenylacetophenone(DMPA), or benzoyl peroxide; azobisisobutyronitrile (AIBN); or an oximeester such as those available under the Irgacure tradename from BASF.

D. The Diamine:

The diamine reactant, or “chain extender” is selected to undergotransimidization with the imide end capped prepolymer upon thermaltreatment of the photocured resin composition. The diamine has thestructure of Formula (XV)

H₂N-L¹-NH₂  (XV)

wherein L¹ is C₂ to C₁₄ hydrocarbylene, including unsubstituted,substituted, heteroatom-containing, and substitutedheteroatom-containing C₂ to C₁₄ hydrocarbylene. Typically, L¹ is anunsubstituted C₂ to C₁₄ alkylene group, such that the diamine is1,3-propanediamine, 1,2-propanediamine, 1,4-butanediamine,1,5-pentanediamine, 1,6-hexanediamine, 1,7-heptanediamine,1,8-octanediamine, 1,9-nonanediamine, 1,10-decanediamine,1,11-undecanediamine, 1,12-dodecanediamine, 1,2-cyclohexanediamine,1,4-cyclohexanediamine, or 4,4′-diaminodicyclohexylmethane.

E. Additives:

The curable resin composition can include any of various additives tofacilitate the curing processes and provide the final product with oneor more advantageous properties. Such additives include, by way ofexample: tougheners; fillers; stabilizers; non-reactive light absorbers;polymerization inhibitors; colorants including dyes and pigments;thickening agent; detectable compounds (e.g., radioactive or luminescentcompounds); metal powders or fibers or other conductive materials;semiconductive particulates or fibers; magnetic materials; flameretardants; and the like. Preferred additives are those described inU.S. Pat. No. 9,598,608 to Rolland et al., incorporated by referenceherein

3. New Compositions of Matter

In one embodiment, the invention provides a curable resin composition asa new composition of matter, where the composition comprises: (i) anend-capped, imide-terminated prepolymer, (ii) at least onephotopolymerizable olefinic monomer, (iii) at least one photoinitiator,and (iv) a diamine, where each of the components are as defined in Athrough E above.

In another embodiment, the invention provides a photocured compositionprepared by irradiating the curable resin composition with actinicradiation of a wavelength effective to cure the photopolymerizableolefinic monomer.

In an additional embodiment, the invention provides a solid compositionof matter prepared by: (a) irradiating the curable resin compositionwith actinic radiation of a wavelength effective to cure thephotopolymerizable olefinic monomer; and (b) thermally treating thephotocured composition provided in (a) with heat under conditions tofacilitate a transimidization reaction between the end-capped,imide-terminated prepolymer and the diamine.

4. Other Embodiments

The invention additionally encompasses other embodiments, wherein aprepolymer other than an end-capped, imide-terminated prepolymer isemployed. The process for forming a 3D specimen from such otherprepolymers is analogous to that described above with regard to theend-capped, imide-terminated prepolymer. That is, the selectedprepolymer is combined with at least one photopolymerizable olefinicmonomer, at least one photoinitiator, and a diamine, to form a curableresin composition. The composition is irradiated under conditionseffective to polymerize the at least one photopolymerizable olefinicmonomer, forming a scaffold that comprises the prepolymer and thepolyolefin with the diamine physically trapped therein. The irradiatedscaffold is then thermally treated at a temperature effective to allow across-linking reaction to occur between the prepolymer and the diamine,providing the solid polymeric structure.

One such embodiment is exemplified in the experimental section herein,in Example 3. That example describes preparation of photocurable esteramide prepolymer, followed by admixture with cyclic trimethylolpropaneformal acrylate as the photopolymerizable monomer and the photoinitiatorTPO. After thorough mixing, the selected diamine, 4,4′-diaminocyclohexylmethane, is added. The stirred resin mixture thus obtained is thenirradiated to polymerize the acrylate monomer followed by heating tocrosslink the prepolymer with the diamine.

The photocurable ester amide prepolymer may be generally represented bythe structure of Formula (XVI)

wherein the various substituents are as follows:

R⁸ and R¹¹ are bulky substituents typically comprising an optionallysubstituted, optionally heteroatom-containing hydrocarbyl group, and maybe alkyl, aryl, or the like. In some embodiments, R⁸ and R¹¹ comprisehydrocarbyl groups of 3-12 carbon atoms, such as isopropyl, t-butyl,cyclohexyl, or the like. R⁸ and R¹¹ may be the same or different,although are typically identical as a simpler synthesis can be employed.

R⁹ and R¹⁰ am difunctional hydrocarbyl groups comprising 1 to 24,typically 2-12, carbon atoms, and may be substituted and/orheteroatom-containing. For example, R⁹ and R¹⁰ may be substituted orunsubstituted lower alkylene or phenylene; if phenylene, the linkage istypically in the form of a p-phenylene link.

L² is an oligomeric hydrocarbyl linker and may be substituted orunsubstituted. L² is defined as for L; see Section 2.A. of this DetailedDescription. Moieties suitable for use as L² are thus identical to thosesuitable for use as L.

As another example, the prepolymer may be anhydride-terminated, havingthe structure of Formula (XVII)

wherein L³ is defined as for L.

Generally, then, the present invention encompasses a dual-cure methodfor forming a solid polymeric structure, where the method comprises:

(a) combining (i) a prepolymer having end groups that upon heatingundergo a covalent reaction with an amine, with (ii) at least onephotopolymerizable olefinic monomer, (iii) at least one photoinitiator,and (iv) a diamine, to form a curable resin composition;

(b) irradiating the resin composition under conditions effective topolymerize the at least one olefinic monomer and provide a polyolefinwithin a scaffold that comprises the prepolymer and the polyolefin withthe diamine physically trapped therein; and

(c) thermally treating the irradiated composition at a temperatureeffective to cause a reaction to occur between the prepolymer end groupsand the diamine.

It will be appreciated that the reaction between the prepolymer endgroups and the diamine results in a crosslinked structure. Thermaltreatment and irradiation are carried out as described previously withrespect to end-capped, imide-terminated prepolymers.

The prepolymer may, accordingly, be generally represented by thestructure of formula (XVIII)

R¹²—L-R¹³  (XVIII)

wherein L⁴ is defined as for L and R¹² and R¹³ are functional groupsthat undergo a covalent reaction with an amine, typically a primaryamine or a secondary amine, optimally a primary amine, e.g., a diaminecontaining two primary amine groups.

In some embodiments, the curable resin composition is added to a buildregion prior to irradiation, the build region dimensionallycorresponding to a predetermined shape and size of the 3D structure tobe fabricated.

In other embodiments, the method is implemented in the context of animproved additive fabrication process that comprises computer-controlledsuccessive formation of layers with dimensions corresponding to a 3Ddigital image, the improvement comprising forming the layers by:

(a) providing an initial curable layer on a substrate, wherein the layercomprises a curable resin composition prepared by the prepolymer with atleast one photopolymerizable olefinic monomer, at least onephotoinitiator, and a diamine;

(b) irradiating the initial layer under conditions effective topolymerize the olefinic monomer and provide a polyolefin within a firstscaffold layer comprising the prepolymer and the polyolefin with thediamine physically trapped therein;

(c) repeating step (a) to provide an additional layer on the firstscaffold layer;

(d) irradiating the additional layer under conditions effective topolymerize the olefinic monomer and provide an additional scaffoldlayer;

(e) repeating steps (c) and (d) until formation of the 3D object iscomplete; and

(f) thermally treating the 3D object at a temperature effective to causea covalent reaction to occur between the prepolymer and the diamine.

It is to be understood that while the invention has been described inconjunction with a number of specific embodiments, the foregoingdescription as well as the examples that follow are intended toillustrate and not limit the scope of the invention.

Example 1 Synthesis of N-(2-Pyrimidyl)phthalimide-Terminated ImidePrepolymer

100.00 g (0.05 mol) of melted anhydrous amine-terminated polyethyleneglycol (molecular weight 2000 g/mol) was added into a 500 mL 4-neckflask equipped with an overhead stirrer, a nitrogen inlet, a thermometerand a reverse Dean-Stark trap with a condenser. Then, 31.02 g (0.10 mol)of 4,4′-oxydiphthalic anhydride was added into the flask, followed byaddition of 39 mL of cyclohexyl pyrrolidinone. The solution was stirredfor 4 hours and an increase in the solution viscosity was observed. Thetemperature was then increased to 175° C. and stirred for an additional12 hours. 9.51 g (0.10 mol) of 2-aminopyrimidine was then added into thesolution and the solution was stirred at 175° C. for an additional 12hours. The viscous liquid was then cooled and poured as the finalproduct.

The two-step reaction is illustrated in Scheme 1:

Example 2 Specimen Formation and Testing Using thePhthalimide-Terminated Imide Prepolymer

(a) General Procedures:

The prepolymer synthesized in Example 1 was polymerized and cured toform 3D) structures as described infra. Tensile properties wereevaluated in accordance with the following ISO standards: ISO 37 (2017)Rubber, Vulcanized or Themplastic-Determination of tensile stress-strainproperties for non-rigid materials; and ISO 527 (2017)Plastics-Determination of tensile properties for rigid materials(International Organization for Standardization, BIBC II Chemin deBlandonnet 8, CP 401, 1214 Vernier, Geneva, Switzerland).

Tensile specimens were loaded onto a GNT5 universal testing machine fromNCS (NCS Testing Technology No. 13. Gaoliangqiao Xiejie, HaidianDistrict, Beijing, 100081, China) mid oriented vertically and parallelto the direction of testing. Cast samples were fully cured using an LEDUV chamber (UV wave length=405±5 nm, intensity-130-150×10² sm/cm²) for60 seconds. Then, the samples were thermally treated in a convectionoven, with specific treatment conditions indicated below. Table 1indicates the types of tensile specimens tested, general materialproperties and the associated strain rate.

Measured dogbone samples that do not rupture in the central rectangularsection were excluded. Samples that broke in the grips or prior totesting were not representative of the anticipated failure modes andwere also excluded from the data.

In order to ensure that the strain rate of the sample was sufficient tocapture deformation, the sample was subjected to a tensile fracture testfor 30 seconds to 5 minutes.

Depending on the type of the material and pursuant to ISO 37 and ISO527, Young's modulus (the slope of the stress-strain diagram at0.05%-0.25% strain), tensile strength at break, tensile strength atyield, percentage of elongation at break, the percentage of elongationat yield, and ultimate tensile strength were measured.

For elastomeric materials having a high elongation at break, ahigh-speed strain rate is required to break it in the usual range of thespecified test. For rigid materials, the ISO standard recommends amodulus of elasticity test rate of 1 mm/min to ensure the loweststrain-at-break will occur within 5 minutes.

TABLE 1 Meterial Specimen Type Standards Type Strain Rate RemarksNon-rigid ISO 37 1A 500 mm/min — Rigid ISO 527-2 5A 10 mm/min — RigidISO 527-2 5A 1 mm/min For Young's Modulus

(b) Specimen Formation and Evaluation:

The UV-curable N-(2-pyrimidyl)phthalimide-terminated imide prepolymerprepared in Example 1 was thoroughly mixed with isobornyl methacrylate,trimethylolpropane trimethacrylate (TMPTMA), and TPO, using an overheadstirrer, to obtain a homogeneous resin. The resin was cast into a 150mm×100 mm×4 mm mold and UV cured for 1 minute. Then, the specimen wassubjected to a thermal cure by heating at 100° C. for 1 hour, followedby heating at 220° C. for 4 hours. The cured elastomeric sheet so formedwas cut into rectangular bars with dimensions of 150 mm×10 mm×4 mm. Theindividual specimens were tested following ISO 527 on a universaltesting machine from NCS for mechanical properties as described above.

The average tensile strength (MPa) and elongation at break (%) areprovided in Table 2, along with the weight percent of each component inthe transimidization reaction mixture.

TABLE 2 Component Weight % N-(2-pyrimidyl) phthalimide-terminated 50.0imide prepolymer Isobornyl methacrylate 35.0 TMPTMA 10.2 TPO 1.04,4′-Diaminodicyclohexyl methane 3.8 Tensile Strength MPa) 16.4Elongation at Break (%) 218

Example 3 Synthesis of a UV-Curable Polyamide Prepolymer

100.0 g (0.05 mol) of melted anhydrous polytetramethylene oxide(molecular weight 2000 g/mol) was added into a 500 mL three-neck flashequipped with an overhead stirrer, a nitrogen inlet and a thermometer.Then, 20.3 g (0.1 mol) terephthaloyl chloride was added to the flask andstirred to give a homogeneous solution with the polytetramethyleneoxide. The temperature was increased to 80° C., and the solution stirredfor 4 hours. After 4 hours, a vacuum was applied. 30 minutes after gasbubbles disappeared from the solution, the vacuum was removed. Thereaction temperature was gradually lowered to 40° C. Then, 37.0 g (0.2mol) 2-(t-butylamino)ethyl methacrylate was added, and the temperaturewas increased to 50° C. for 2 hours. The resulting viscous liquid wasthen poured out as the reaction product.

The two-step reaction is illustrated in Scheme 3 (“Ph” represents phenyland “t-Bu” represents tertiary butyl).

Example 4 Specimen Formation and Testing Using the Polyamide Prepolymer

The general procedures of Example 2 were followed here in the formationand evaluation of a specimen from the UV-curable polyamide prepolymerprepared in Example 3.

The prepolymer of Example 3 was thoroughly mixed with cyclictrimethylolpropane formal acrylate and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) photoinitiator, using an overhead stirrer, toobtain a homogeneous resin. Then, 4,4′-diaminocyclohexyl methane wasadded and mixing was continued for another 10 min. The resin was castinto a 150 mm×100 mm×4 mm mold and UV cured for 1 minute. Then, thespecimen was subjected to a thermal cure by heating at 100° C. for 1hour, followed by heating at 220° C. for 4 hours. The cured elastomericsheet so formed was cut into rectangular bars with dimensions of 150mm×10 mm×4 mm. The individual specimens were tested following ISO 527 ona universal testing machine from NCS for mechanical properties asdescribed above.

The average tensile strength (MPa) and elongation at break (%) areprovided in Table 3, along with the weight percent of each component inthe transamidation reaction mixture.

TABLE 3 Component Weight % UV-Curable polyamide prepolymer 70.0 Cyclictrimethylolpropane formal 24.2 acrylate TPO 1.0 4,4′-Diaminodicyclohexylmethane 4.8 Tensile Strength MPa) 4.6 Elongation at Break (%) 236

What is claimed is:
 1. In a method for forming a three-dimensionalobject using an additive fabrication process that comprisescomputer-controlled successive formation of layers on a substrate withdimensions corresponding to a 3D digital image, the improvement whichcomprises forming the layers by: (a) providing an initial curable layeron a substrate, wherein the layer comprises a curable resin compositionprepared by combining an end-capped, imide-terminated prepolymer, aphotopolymerizable olefinic monomer, at least one photoinitiator, and adiamine; (b) irradiating the initial layer under conditions effective topolymerize the olefinic monomer and provide a polyolefin within a firstscaffold layer comprising the prepolymer and the polyolefin with thediamine physically trapped therein; (c) repeating step (a) to provide anadditional layer on the first scaffold layer; (d) irradiating theadditional layer under conditions effective to polymerize the olefinicmonomer and provide an additional scaffold layer; (e) repeating steps(c) and (d) until formation of the 3D object is complete; and (f)thermally treating the 3D object at a temperature effective to cause atransimidization reaction to occur between the prepolymer and thediamine, wherein the prepolymer has the structure of Formula (IV)

wherein R² and R⁴ are imide end-capping groups that can be removed in atransimidization reaction.
 2. The method of claim 1, wherein L ispolyethylene, such that the prepolymer has the structure of Formula (V)

where n is the number of oxyethylene monomer units in L.
 3. The methodof claim 2, wherein R² and R⁴ are both 2-pyrimidinyl, such that theprepolymer has the structure of Formula (X)


4. The method of claim 1, wherein L is polyethylene, such that theprepolymer has the structure of Formula (VI)

where n is the number of ethylene monomer units in L.
 5. The method ofclaim 4, wherein R² and R⁴ are both 2-pyrimidinyl, such that theprepolymer has the structure of Formula (XI)


6. The method of claim 1, wherein the prepolymer has a weight averagemolecular weight in the range of about 500 to about
 5000. 7. The methodof claim 6, wherein the prepolymer has a weight average molecular weightin the range of about 1000 to about
 3000. 8. The method of claim 1,wherein the polymerizable olefinic monomer is an acrylate ormethacrylate monomer.
 9. method of claim 8, wherein the acrylate ormethacrylate monomer has the structure of Formula (XIV)

wherein R⁵ is H or CH₃ and R⁶ is C₁ to C₃₆ hydrocarbyl, substituted C₁to C₃₆ hydrocarbyl, heteroatom-containing C₁ to C₃₆ hydrocarbyl, orsubstituted and heteroatom-containing C₁ to C₃₆ hydrocarbyl.
 10. Themethod of claim 9, wherein R⁶ comprises a C₆-C₃₆ alicyclic moiety. 11.The method of claim 10, wherein R⁶ is isobornyl.
 12. The method of claim1, wherein the diamine has the structure of Formula (XV)H₂N-L¹-NH₂  (XV) where L¹ is C₂ to C₁₄ hydrocarbylene, substituted C₂ toC₁ hydrocarbylene, heteroatom-containing C₂ to C₁₄ hydrocarbylene, orsubstituted and heteroatom-containing C₂ to C₁₄ hydrocarbylene.
 13. Themethod of claim 12, wherein L¹ is unsubstituted C₂ to C₁₄ alkylene. 14.The method of claim 1, wherein the irradiating is carried out usingactinic radiation.
 15. The method of claim 14, wherein the actinicradiation is ultraviolet radiation having a wavelength selected tofacilitate polymerization of the photopolymerizable olefinic monomer.16. The method of claim 15, wherein the wavelength is about 405 nm. 17.The method of claim 15, wherein the ultraviolet radiation is applied atan intensity in the range of about 13,000 to 15,000 μm/cm².
 18. Themethod of claim 1, wherein the thermal treatment is carried out at atemperature in the range of about 75° C. to about 300° C.